Add option to include average value of buff over time in stats

For certain, simple things like Convention of Elements and the Barbarian's Ruthless passive, it would be nice if in addition to "Include in stats" there was an option along the lines of "Include average in stats." So for the Barbarian who has four elements, the average value over time of the buff from CoE for a specific element would be 25% of the full value. Ruthless ("You deal 40% additional damage to enemies below 30% health"), averages out to 12% additional damage.